Methods and apparatus for generating and processing transmitter signals

ABSTRACT

Transmitter signals are modulated with one or more codes which may represent a pulse even though the code(s) are not shaped as pulses. The code(s) may be generated by defining a pulse by its Fourier components, and then adding random phases to the Fourier components. A time-domain signal may then be created, which may serve as the code to be modulated on a carrier wave. Upon reflection of the transmitter signal, the received signal may be processed by a receiver to recover the pulse. The time-of-flight of the transmitter signal can then be determined, enabling distance measurements to be made.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application claims the benefit under 35 U.S.C. § 119(e) of U.S.provisional patent application Ser. No. 61/002,546 (the '546application), entitled “LIDAR System,” and filed on Nov. 12, 2007. The'546 application is incorporated herein by reference in its entirety.

BACKGROUND

1. Field

The technology described herein relates to apparatus and methods forgenerating and processing coded transmission signals, and variousapplications of such apparatus and methods.

2. Discussion of Related Art

Distance measurements to an object can be made by sending and receivingtransmission signals. A transmitted signal is sent from a transmittertoward the object. The transmitted signal is reflected by the object anddetected by a receiver positioned at the same location as thetransmitter. Assuming some knowledge about the speed of propagation ofthe transmitted and reflected signals, the distance to the object can becalculated by determining the amount of time between when the signal istransmitted by the transmitter and when it is received by the receiver.

BRIEF SUMMARY

According to one aspect, a method of producing a coded continuous wavetransmitter signal is provided. The method comprises producing acontinuous wave carrier signal, and modulating the continuous wavecarrier signal with a code to produce the coded continuous wavetransmitter signal, the code representing a pulse in non-pulse form.

According to another aspect, a method comprises transmitting acontinuous wave transmitter signal comprising a continuous wave carriersignal modulated with a code representing a pulse in non-pulse form. Themethod further comprises receiving the continuous wave transmittersignal, and processing the continuous wave transmitter signal to recoverthe pulse.

According to another aspect, a transmitting system comprises a computingengine configured to generate a code, the code representing a pulse innon-pulse form, and a signal generator configured to produce a signalmodulated by the code.

According to another aspect, a system comprises a transmitter configuredto transmit a transmitter signal comprising a continuous wave carriersignal modulated with a code representing a pulse in non-pulse form. Thesystem further comprises a receiver configured to receive thetransmitter signal and process the transmitter signal to recover thepulse.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a system which can determine the distance to an object,according to one embodiment;

FIG. 2 is a flowchart of a method of generating and processing atransmission signal, according to one embodiment;

FIG. 3 is a flowchart of a method of generating a code representing apulse, as used in the method of FIG. 2, according to one embodiment;

FIGS. 4A and 4B illustrate one non-limiting example of an impulse, and atime domain code which may be used in the methodology illustrated inFIG. 3;

FIG. 4C illustrates an exemplary transmitter signal formed with a codeof the type illustrated in FIG. 4B;

FIG. 5 is a flowchart of an example of a method of processing a signalto recover a pulse, as used in the method of FIG. 2;

FIGS. 6A and 6B illustrates examples of pulses reconstructed from areflected transmitter signal using the method of FIG. 5;

FIG. 7 is a transmitter/receiver system capable of operating accordingto the method of FIG. 2, according to one embodiment;

FIG. 8 is an example of a type of graph that can be used to facilitatedetermination of the timing of a received transmitter signal, accordingto one embodiment;

FIGS. 9A-9D illustrate examples of transmitter signals shifted relativeto each other by a constant amount of delay, according to oneembodiment;

FIG. 9E illustrates a signal that can be received by a receiver,corresponding to the combination of the signals shown in FIGS. 9A-9D;

FIG. 9F illustrates pulses reconstructed from the signal of FIG. 9E;

FIG. 10A illustrates a system including a single transmitter andmultiple receivers, according to one embodiment;

FIG. 10B illustrates a system including multiple transmitters and asingle receiver, according to another embodiment;

FIG. 10C illustrates a system including a single transmitter capable ofscanning a field of view, and a single receiver, according to oneembodiment;

FIGS. 11A and 11B illustrate a received transmitter signal with clippingand a pulse reconstructed from the received transmitter signal,respectively, according to one embodiment; and

FIG. 12 is a flowchart illustrating a method of generating andprocessing coded continuous wave signals, according to one embodiment.

DETAILED DESCRIPTION

Apparatus and methods are presented which may be used to effectivelyoperate a continuous wave transmission system as a pulsed system, withlittle or no alteration of the continuous wave nature of thetransmission signals. Transmitter signals may be coded with a code, orsequence, which includes the information of a pulse in a non-pulse form,such as a noise form. Thus, coding a continuous wave carrier signal withthe code may do little, or nothing, to alter the continuous wave natureof the transmitter signal, while carrying the information of the pulse.Thus, benefits of continuous wave transmission systems, such as lowercost, design simplicity, and more easily achieved power requirements(e.g., lower peak power to average power ratios), may be realized, aswell as benefits of pulsed-transmission modalities, such as highaccuracy, and the ability to detect multiple reflections, to name a few.Such apparatus and methods may find use in range-finding systems (i.e.,distance measuring systems) or other contexts. The methods and systemsmay be implemented as spread spectrum or ultra wideband technologies,among others.

According to an aspect of the invention, a continuous wave (CW) carriersignal is encoded with a code representing a pulse, in non-pulse form.Any type of pulse may be used, as the various aspects of the inventionare not limited to use with any particular type of pulse. Examples ofsuitable pulses may include an impulse, a square pulse, or a trianglepulse, among others. An example of a non-pulse form into which the pulsemay be transformed to form the code is a Gaussian noise-like sequence.However, the various aspects and embodiments of the invention are notlimited to use with any particular non-pulse forms, as there are manynon-pulse forms into which a pulse may be transformed. Furthermore, thetype of non-pulse form used may be chosen to have beneficialcharacteristics. For example, as compared to a pulse, the code may havea low peak-to-average power ratio. Also, the transformation of the pulseinto a non-pulse form may be completed using any suitable type oftransformation, examples of which may include a Fourier transform, aLaplace transform, or a Hadamard transform, among others. Thetransformation may comprise scrambling values of the pulse, modifyingthe pulse with a key formed of a set of numbers, or any other suitablesteps.

The coded signal, comprising the continuous wave carrier signalmodulated with the code, may then be transmitted by a transmitter andreceived by a receiver. The receiver may then perform a reversetransformation on the received signal to recover the pulse, i.e., toundo the transformation of the pulse into a non-pulse form. In thismanner, a transmitter-receiver system may effectively operate as iftransmitting and receiving a pulse, while in actuality the signalstransmitted and received do not resemble pulses. It should beappreciated that, according to some embodiments, the receiver may haveknowledge of the type of transformation used by a transmitter whentransforming a pulse into a non-pulse form to form a code, so that thereceiver may accurately undo the transformation when receiving thetransmitted signal. Such knowledge may be provided in some embodimentsby sending information between the receiver and transmitter, by usingshared components for a receiver and transmitter, or by any othersuitable manner.

FIG. 12 illustrates one example of a method for transmitting andprocessing signals, according to one embodiment. As shown, the method1200 may include a transmitting process 1202, and a receiving process1204. The transmitting process 1202 may begin at 1206 with generating acode, or sequence, by transforming a pulse into a non-pulse form. Forexample, according to one embodiment, the pulse, which may be any typeof pulse (e.g., an impulse, a square pulse, a triangle pulse, or anyother type of pulse) may be a time domain signal, which may betransformed into a different domain. Once transformed into the otherdomain, the pulse may be modified, for example by randomizing,scrambling, or otherwise altering values of the pulse. The modifiedpulse may then be further modified to return it to a time domain signal,thus completing act 1206. The modification may result in the pulse nolonger resembling a pulse in form, but rather resembling noise, or someother non-pulse form which may have beneficial characteristics in termsof use as a transmission and reception signal. It should be appreciatedthat act 1206 may be performed in various manners, and that not allmanners of performing act 1206 may involve moving between differentsignal domains (e.g., between time domain and frequency domain).

Subsequently, the code, which again may carry the information of apulse, but in non-pulse form, may then be used to modulate a continuouswave carrier signal at 1208. At 1210, the transmitter signal, comprisingthe continuous waver carrier signal coded with the code, may then betransmitted. According to the embodiment of FIG. 12, the transmittedsignal may be reflected from an object, although it should beappreciated that such reflection need not occur in all embodiments.Then, at 1214, the reflected signal may be received by a receiver.

At 1216, the received signal may be processed to recover the pulse bytransforming the code of the received signal into the pulse. In someembodiments, the transformation of the code into the pulse may compriseperforming the reverse transformation of the transformation used in act1206 to form the code from the pulse. It should be appreciated that,according to some embodiments, the steps taken to transform the codefrom the received signal into the pulse may not be an exact reverse ofthe transformation used to transform the pulse into the code at 1206.Rather, as used herein, a reverse transformation may include atransformation which undoes the effects of a different transformation,regardless of whether the reverse transformation actually entailsperforming the same steps of the different transformation in a reverseorder.

According to one aspect of the invention, a continuous wave carriersignal may be modulated with a code, or sequence, representing arandomized version of a pulse, and then transmitted. The transmittedsignal may be reflected from an object and received by a receiverpositioned near the transmitter. The received signal may be processed torecover the pulse, from which the time-of-flight of the pulse may bedetermined. The distance from the transmitter and receiver to the objectmay then be determined using the time-of-flight of the pulse and thespeed of propagation of the pulse.

FIG. 1 illustrates one example of a system according to one embodiment,which may utilize one or more of the methods described above. As shown,the system 100 comprises a transmitter 102 and a receiver 104. Thetransmitter 102 and receiver 104 may be positioned in substantially asame location so that they each are located substantially the samedistance from any surrounding objects. The transmitter 102 and receiver104 may be distinct, may be the same (i.e., a transceiver that operatesas both a transmitter and a receiver), may share some components whilehaving some distinct components, or may take any suitable form, as thevarious aspects of the invention are not limited in this respect.

The transmitter 102 may generate and transmit a transmitter signal 106,which may be a coded continuous wave transmitter signal, as describedfurther below. The transmitter signal 106 may impact, and be at leastpartially reflected from, an object 108, thus generating a reflectedsignal 110, i.e., a reflected version of the transmitter signal 106. Theobject 108 may be a car, a tree, a person, or any other type of object,as the various aspects of the invention are not limited to use with anyparticular type of object. Also, the object 108 may be stationary ormoving. The reflected signal 110 may be received by the receiver 104,from which the distance x₁ between the receiver and transmitter and theobject 108 may be determined using Eq. (1):

x ₁=(vt/2)  Eq. (1)

where v is the velocity of the transmitter signal 106 and the reflectedsignal 110, which is presumed to be the same for both, and t is the timebetween when the transmitter signal 106 is transmitted by transmitter102 and the time when the reflected signal 110 is received by receiver104.

According to an aspect of the invention, the transmitter signal 106, andtherefore the reflected signal 110, may be coded continuous wavesignals. The code may represent a pulse in non-pulse form, for examplebeing a randomized version of a pulse. For example, as will be discussedin greater detail below, a pulse (e.g., a delta function, a squarepulse, a triangle pulse or any other type of pulse) may be transformedmathematically into a randomized signal, for example a signal thatappears to be noise. This “noise” signal may serve as the code to bemodulated on a continuous wave carrier signal to produce the codedcontinuous wave signal 106. Then, as mentioned previously, the reflectedsignal 110, which may therefore also contain the code modulated on acontinuous wave carrier signal, may be processed to recover the pulse.FIG. 2 illustrates one example of a method for generating and processinga coded continuous wave signal, such as the transmitter signal 106 andreflected signal 110.

The method 200 comprises several acts which may be performed as part ofa transmitting process 202 and several acts which may be performed aspart of a receiving process 204. Method 200 is not limited in the typeof hardware and/or software which may be used to perform the variousacts enumerated, but rather may be performed in any suitable manner. Forexample, the acts of the transmitting process 202 may be performed bythe same hardware and/or software as the acts of the receiving process204, by different hardware and/or software, or by any suitablecombination of shared hardware and/or software, as the methodology isnot limited in this respect.

As shown, the method 200 begins with the transmitting process 202, andnamely with generating a code representing a pulse at 206. Generatingthe code may comprise generating a randomized version of a pulse, aswill be described in further detail below with respect to FIG. 3. Itshould be appreciated that while the methodology of FIGS. 2-3 shows anddescribes generating a code, other embodiments do not involve actualgeneration of the code. Rather, according to some embodiments, the codemay be read out from a memory containing one or more suitable codes, alibrary, or provided in any other suitable manner.

Once the code is generated, a carrier signal may be modulated with thecode at 208. The carrier signal may be a continuous wave carrier signal,for example produced by a continuous wave transmitter. The code may belimited in time, having any suitable duration. For example, in someembodiments the duration of the code may be chosen to be longer, andsometimes significantly longer, than the maximum expected time of flightfor the code, from the time the code is transmitted by a transmitter tothe time the code is received by a receiver. For example, the durationof the code may be 2 nanoseconds, 2 microseconds, 4 microseconds, 10microseconds, 200 microseconds, a few milliseconds, or any othersuitable duration, as the various aspects described herein are notlimited to using codes of any particular duration.

The continuous wave carrier signal may be modulated with a singleoccurrence of the code, or may be modulated with multiple occurrences ofthe code. If the continuous wave carrier signal is modulated withmultiple occurrences of the code, the multiple occurrences may beseparated in time, for example by modulating the continuous wave carriersignal with two 1-second long occurrences of the code separated by fiveseconds, or may be continuously repeating such that there is no time gapbetween the occurrences of the code on the carrier signal.

The coded transmitter signal, i.e., the continuous wave carrier signalmodulated with one or more occurrences of the code generated at 206, maythen be transmitted at 210, for example by transmitter 102 in FIG. 1, orby any other suitable transmitter. As will be described in furtherdetail below, the code may not alter, or may not significantly alter,the continuous nature of the carrier signal, such that the transmittersignal may be produced by a continuous wave transmitter. For example,the code may include randomized sample points of a pulse, and mayapproximate noise in some embodiments. Thus, the ratio of peak power toaverage power of the code may not be large, for example being less than10, or even lower in some embodiments.

After being transmitted, the transmitter signal may be reflected from anobject at 212. It should be appreciated that according to someembodiments, the transmitted signal may undergo multiple reflections,i.e., be reflected from multiple objects, thus generating multiplereflected signals. The method 200 may apply equally well to scenariosinvolving multiple reflections.

The method 200 may then progress to the receiving process 204. Inparticular, the reflected signal(s) generated at 212 may be received at214 by any suitable receiver. The received signal(s) may then beprocessed, as described in further detail below with respect to FIG. 5,to recover the pulse represented by the code produced at 206. Theprocessing may be performed by the receiver, or may be sent by thereceiver to any suitable processing device, such as a computer, anapplication specific integrated circuit (ASIC), or any other suitablehardware, software, or combination thereof, for processing the receivedsignal(s). As mentioned previously, the recovered code and/or pulse maybe used to determine the time-of-flight of the pulse represented by thecode, from which a determination of the distance to the reflectingobject can be made. However, the methodology illustrated in FIG. 2 isnot limited to using the recovered code and/or pulse for any particularpurpose.

Also, as mentioned, it should be understood that the acts of method 200may be performed on multiple signals simultaneously. For example, asmentioned, the transmitted signal may undergo multiple reflections, sothat act 214 may involve receiving multiple signals, and act 216 mayinvolve processing the multiple signals to recover pulses from each ofthe received signals. Alternatively, multiple signals may be transmittedby multiple transmitters, as will be described in greater detail withregard to FIGS. 9A-9D, and the receiving process may be performed on allof the signals from the various transmitters.

FIG. 3 illustrates one exemplary method of generating a code formodulating a transmitter signal, as shown at 206 in FIG. 2. The code mayrepresent a pulse while not taking the form of a pulse, and according tosome embodiments represents a randomized version of a pulse. Asdescribed earlier, it may desirable in some contexts to send a pulsefrom a transmitter, since the distance to an object can be determined bymeasuring the time-of-flight of the pulse. However, there are drawbacksassociated with conventional systems and methods of sending a pulse.Conventional systems are often complex and/or costly as the hardwareneeded to generate a pulse, and the large amplitude variationsassociated therewith, can itself be complex and/or costly. By contrast,systems for generating continuous wave transmission signals may besimpler, less costly, and less subject to failure. Thus, according to anaspect of the invention, the code used to modulate the continuous wavecarrier signal may not actually take the form of a pulse, but rather maycarry the information of a pulse in a non-pulse form. Thus, modulating acontinuous wave carrier signal with the code may not alter, or notsignificantly alter, the continuous wave nature of the carrier signal.

Referring again to FIG. 3, act 206 from FIG. 2 of generating a coderepresenting a pulse may therefore comprise, at 302, defining a pulse byits Fourier components. Any type of pulse may be used for such purposes,and therefore the pulse defined at 302 may be a square pulse, a trianglepulse, an impulse, or any other type of pulse. The characteristics ofthe pulse, such as duration, shape, and amplitude, may be chosen asdesired for a particular system and application, as the various aspectsof the invention are not limited to utilizing any particular types ofpulses. For ease of explanation, and without limiting the scope of anyof the aspects described herein, an impulse (i.e., a delta function)will be described as an exemplary pulse. FIG. 4A illustrates an impulse401, having substantially zero width, which has been normalized to havean amplitude of approximately one in terms of generic units u (e.g.,voltage in Volts), and which may be used for purposes of explanationwith regard to FIG. 3. It should be appreciated that such normalizationis optional, and that the various aspects of the invention are notlimited to the use of normalized pulses. Furthermore, it should beappreciated that FIG. 3, and the other methods described herein, are notlimited to use with impulses.

The act 302 of defining the impulse by its Fourier components may bedone using integrals, or in practice may be done using a summation, asthe various aspects of the invention are not limited in this respect.For purposes of explanation, the pulse may be resolved over a time, orduration, T. The pulse may be defined by a finite number of samplepoints over the duration T, corresponding to the Fourier components ofthe pulse. Any number of sample points may be used. In some embodimentsthe method of FIGS. 2-3 may be implemented using a system comprising ananalog-to-digital converter (A/D converter, also referred to as a ADC)and/or a digital-to-analog converter (D/A converter, also referred to asa DAC), as will be described below in reference to FIG. 7. In suchsituations, the number of sample points, N_(s), over which the pulse isresolved may be given by N_(s)=F_(s)T, where F_(s) is a sample rate, forexample corresponding to the sample rate of an A/D converter or D/Aconverter.

After defining the impulse by its Fourier components, at 302, the act206 of producing a code may further comprise, at 304, generatingmultiple random phases to be added to the Fourier components of theimpulse from 302. The random phases may be generated by a random numbergenerator, by hand, or in any other suitable manner, as the variousaspects of the invention are not limited in this respect. According toone embodiment, a random phase vector φ_(n) includes N_(s)/2 phases (fora real signal), to be randomly distributed among the N_(s) Fouriercomponents defining the pulse from 302.

According to the non-limiting example of FIG. 3, the generated randomphases are then added to the Fourier components of the impulse. Onephase may be added to each of the Fourier components. At 308, an inversefast Fourier transform (IFFT) is then performed on the Fouriercomponents randomized with the random phases, thus producing a timedomain signal. Equation 2 shows an example of the resulting time domainsignal, which, as will be described in greater detail below, maycorrespond to the signal sent from a computing engine to a D/Aconverter:

$\begin{matrix}{{{s\left( t_{m} \right)} = {\sum\limits_{n = {{- {Ns}}/2}}^{{{Ns}/2} - 1}{\exp \left\lbrack {- {\left( {{n\frac{2\pi}{N_{s}}m} + \varphi_{n}} \right)}} \right\rbrack}}}{{{where}\mspace{14mu} \varphi_{n}} = {{\varphi_{- n}^{*}\mspace{14mu} {and}\mspace{14mu} t_{m}} = {m\; \tau_{s}}}}} & {{Eq}.\mspace{14mu} (2)}\end{matrix}$

wherein φ_(n) is the random phase vector, m is the sample point number,τ_(s) is the sample time, and t_(m) is the signal at the m^(th) point intime.

The signal of Eq. (2) has a low “peak-to-average” ratio. In particular,because the phases of the Fourier components are randomized prior totaking the IFFT, the energy of the pulse may be distributedsubstantially evenly across the duration of the code, and the ratio ofpeak energy to average energy may be less than approximately ten, orsmaller. In some embodiments, then, a signal generator (e.g., a laser, aradio wave generator, etc.) may be nominally operated with a lowpeak-to-average ratio (e.g., a peak-to-average power less than 10). Inaddition, the signal of Eq. (2) is periodic with interval T. For aperfectly random phase, the output amplitude is Gaussian, distributedwith a root-mean-square (rms) amplitude of 1. In some embodiments, a DCterm (of amplitude between 1-4, or any other suitable amplitude) may beadded to the signal of Eq. (2) prior to modulating the carrier signalwith the signal of Eq. (2), to avoid substantial clipping. However, themethod of FIG. 3 is not limited in this respect.

It should also be appreciated that Eq. (2) is one non-limiting exampleof a suitable code that may be generated according to the methodology ofFIG. 3. Other forms of codes are also possible. For example, analternative suitable code may be given by:

$\begin{matrix}{{{s\left( t_{m} \right)} = {\sum\limits_{n = {{- {Ns}}/2}}^{{{Ns}/2} - 1}{{A_{n}\left( N_{s} \right)}{\exp \left\lbrack {- {\left( {{n\frac{2\pi}{N_{s}}m} + \varphi_{n}} \right)}} \right\rbrack}}}}{where}} & {{Eq}.\mspace{14mu} (3)} \\{{A_{n}\left( N_{s} \right)} = {\exp \left( {\frac{- 1}{2}\frac{n^{2}}{N_{s}^{2}}} \right)}} & {{Eq}.\mspace{14mu} (4)}\end{matrix}$

and wherein the phase vector is defined by:

$\begin{matrix}{{\varphi_{n}\left( {c,p} \right)} = {{c\left( \frac{n}{\pi} \right)}^{p}{\sin (n)}}} & {{Eq}.\mspace{14mu} (5)}\end{matrix}$

For particular values of c and p in Eq. (5), a Gaussian noise-likeoutput is created. Thus, the pair (c,p) may be chosen from a large setof possible choices and still provide a unique code to atransmit-receive pair, even though the phase vector is not randomized.

FIG. 4B illustrates a time domain code 402 which may be generated byapplying the methodology of FIG. 3 to the impulse 401 of FIG. 4A, andwhich may be used to modulate a continuous wave carrier signal. They-axis of FIG. 4B is given in terms of the output state of a 12-bitdigital-to-analog (D/A) converter (alternatively referred to as a“DAC”), which is one example of a component which may used in producingthe code. Thus, the actual units of the y-axis may correspond to anysuitable voltage.

Various characteristics of the code 402 shown in FIG. 4B may bementioned. For example, it should be appreciated that the codesdescribed herein need not be produced using a D/A converter. Also, itshould be appreciated that the code shown in FIG. 4B includes a DCoffset of approximately 2000, i.e., has been scaled, to prevent clippingof the signal. Such scaling is optional, and need not be done in everyinstance. In addition, the code in FIG. 4B contains 4096 sample points,although the methods described herein are not limited to using codes ofthis length. FIG. 4B illustrates how, in some embodiments, the generatedcode may appear similar to noise.

FIG. 4C illustrates an example of a transmitter signal 404, for exampleoutput by a laser, that includes a continuous wave carrier signalmodulated with a code, such as the code illustrated in FIG. 4B. Theamplitude of the signal is given in generic units (u), e.g., a voltagein milliVolts, Volts, or any other suitable amplitude, since it will beappreciated that the absolute magnitude of the signal may depend onvarious components of a system generating such a signal, so that thevarious aspects of the invention are not limited to working with anyparticular magnitudes of signals. The signal may be periodic with aperiod T, for example. It should be appreciated by reference to FIG. 4Cthat a transmitter signal according to various aspects of the inventiondoes not contain a pulse in form, even though it may contain theinformation of a pulse.

FIG. 5 illustrates one non-limiting embodiment of the act 216 in FIG. 2for processing a coded transmitter signal reflected from an object.According to some embodiments, the signal received from the target,i.e., the reflected signal, is periodic with an interval T. For example,as mentioned, FIG. 4C illustrates an example of an output from a signalgenerator according to one embodiment, which may be periodic. The signalreceived from the target may be substantially the same in form, withsome possible attenuation of the amplitude. As shown in FIG. 5, act 216may optionally begin at 502 by summing some number, Nr, of copies of thereceived signal. For example, the samples N_(s) for each interval T ofthe received signal may be stored and added to the samples from the nextinterval of the received signal. Thus, the periodic signal may addcoherently, while noise in the signal may add incoherently. The noise inthe signal may arise from the environment, from circuit components(e.g., a photodetector, a transimpedance amplifier, or other circuitryof a receiving system), or from other sources.

As mentioned, the summation performed at 502 in FIG. 5 is optional, andneed not be performed in all situations. The summation may improve thesignal-to-noise ratio (SNR) of the received signal by an amount equal tothe square root of the number of additions performed. Thus, the moreadditions performed, the better the improvement of the signal.

Subsequently, at 504, a Fourier transform may be performed on thereceived signal, or in the non-limiting embodiment of FIG. 5, on thesummed received signal formed at 502. The resulting Fourier componentsmay each include a phase, such as a random phase, corresponding to thephases added at act 306 in FIG. 3 when generating the code.

Therefore, the methodology illustrated in FIG. 5 may proceed at 506 byremoving the random phases from the Fourier components of the summedreceived signal from 504. This may be accomplished by subtracting therandom phases from the Fourier components of the summed received signal,or by multiplying each of the Fourier components by the complexconjugate of the random phase term exp[−i _(n)] of Eq. (2). According tothis non-limiting embodiment, the random phase subtracted from each ofthe Fourier components at 506 corresponds to the random phase added toeach of the corresponding Fourier components at 306 in FIG. 3, such thatthe result of 506 is to produce Fourier components that do not have anyrandom phase value. For example, the phase vector φ_(n) used torandomize the transmitted signal at 306 in FIG. 3 is subtracted from theFourier transformed signal from act 504.

Subsequently, at 508, an IFFT of the Fourier components produced at 506may be performed to recover the pulse defined at 302 in FIG. 3. The IFFTresults in a time domain signal, as shown in Eq. (6):

$\begin{matrix}{{S_{rec}\left( t_{m} \right)} = {\left( {\frac{\eta^{\prime}}{z^{2}}\sqrt{\frac{1}{RT}}} \right){\sum\limits_{n = {{- {Ns}}/2}}^{{{Ns}/2} - 1}{{\exp \left\lbrack {- {\left( {{n\frac{2\pi}{N_{s}}\left( {m + \frac{2z}{c}} \right)} + \varphi_{n}} \right)}} \right\rbrack}{\exp \left\lbrack {{+ }\; \varphi_{n}} \right\rbrack}}}}} & {{Eq}.\mspace{14mu} (6)}\end{matrix}$

in which R is the update rate (e.g. the rate at which the transmittedsignal is transmitted), T is the total code duration, or length, RT isthe number of additions performed at act 502, m is the sample pointnumber, z is the distance from the transmitter/receiver to thereflecting object, c is the speed of propagation of the transmitted andreflected signals, and η′ is an attenuation coefficient. The term

$\left( {\frac{\eta^{\prime}}{z^{2}}\sqrt{\frac{1}{RT}}} \right)$

is the result of attenuation of the signal from a distant target andaveraging of the received signal. The term 2z/c corresponds to the delayto the target, with z being the distance to the target (or object), andc being the speed of propagation. The last term, exp[+iφ_(n)], is theoperation of multiplication by the original “randomized” phase vectorafter taking the FFT of the received signal. The resultant signalS_(rec)(t_(m)) is a “delta function” at a delay corresponding to 2z/c orat an array location

${m_{z} = \frac{2z}{c\; \tau_{s}}},$

where m_(z) is the sample point number, and τ_(s) is the sample time.

FIG. 6A illustrates an example of a resulting reconstructed pulse 602produced by applying the methodology of FIG. 5 on a signal such as thatshown in FIG. 4C, which is approximately a delta function. The units ofamplitude are generic units (u), given that the absolute magnitude ofthe amplitude (i.e., the voltage) may differ depending on the type ofsystem used to implement the method. FIG. 6B, which also shows anamplitude in generic units (u), illustrates another example of areconstructed pulse 603 attained by processing a signal such as thatshown in FIG. 4C using the methodology of FIG. 5, using the assumptionthat the transmitted signal is reflected from an object located 50meters from the transmitter/receiver. As will be described in connectionwith FIG. 7, the receiver may include circuitry having a finite samplingrate, such as an A/D converter. The reconstruction of FIG. 6B assumes asampling rate of 125 MHz. As shown, the recovered signal is not exactlyan impulse, but rather is spread across multiple samples, or bins, withthe peak falling between the 10^(th) and 11^(th) bins. The samples, orbins, correspond to the sampling rate of an A/D converter, such as A/Dconverter 724 in FIG. 7. As will be described in connection with FIG. 8,below, one aspect of the invention provides a method of determining theplacement of the reconstructed pulse within the bins.

Several features of the methodology of FIGS. 2, 3, and 5 should bementioned, as well as features of the resulting signals. For example, itshould be appreciated that the phase vector φ_(n) is unique to atransmit-receive pair, and therefore may be used as a “key” to key atransmitter and receiver to each other, thus enabling them to operateaccurately in the presence of other transmitters and receivers.Operating on the received signal with different phases φ_(n) than thoseused to generate the transmitter signal will not result in thereconstructed delta function. In this manner, the phase φ_(n) mayoperate as a “key,” since the receiver may not recover the pulse withouthaving the correct phase values, i.e., the correct “key.” Thus, themethod shown in FIGS. 3 and 5 automatically provides a unique key for atransmitter-receiver pair. It should be appreciated that while thephases φ_(n) may be one type of key, that other types of keys may beused to operate on a pulse in generating the code, and then be used by areceiver in recovering the pulse from the transmitter signal. Thus,phase values φ_(n) are merely one non-limiting example of a key that canbe used to generate a code by transforming a pulse into a non-pulseform.

In addition, it should be appreciated that the resultant “peakamplitude” of the delta function reconstructed according to the methodof FIG. 5, for example the reconstructed delta function of FIG. 6A, mayhave an amplitude that differs from the amplitude of the transmittedsignal, for example due to attenuation or other factors. As onenon-limiting example, the reconstructed delta function may have aneffective amplitude of

$\frac{\sqrt{N_{s}}}{3}P_{a}$

where P_(a) is the average power, and N_(s) is the number of samplepoints of the code. The factor of one-third (i.e., ⅓) may be a practicalconsequence of implementing the methods described herein, for example inthat the factor of one-third may correspond to the fact that a DC termmay be added to the transmitter output signal (e.g., the signal of FIG.4C includes a DC offset of approximately 3) to avoid clipping of thetransmitter output. Thus, it should be appreciated that the factor of ⅓is just one example, and that other values (e.g., ½, ¼, or other values)may result from other systems. The average power P_(a) may be given byP_(a)=(2π)^((1/2))P_(o)R, where P_(o) is the peak power and R is theupdate rate.

Furthermore, applying the methodology of FIG. 5 may result in asatisfactory SNR of the system. For example, the SNR may be given by Eq.(7):

$\begin{matrix}{{S\; N\; R} = {{\frac{\eta^{\prime}}{z^{2}}\left( \frac{\sqrt{\frac{1}{TR}}\frac{\sqrt{N_{s}}}{3}P_{a}}{\sqrt{\frac{F_{s}}{2}}} \right)} = {{\frac{\eta^{\prime}}{z^{2}}\frac{P_{a}}{3}\sqrt{\left( \frac{2}{R} \right)}} = {\frac{\eta^{\prime}}{z^{2}}\frac{P_{a}}{3}\sqrt{\left( \frac{2}{R} \right)}}}}} & {{Eq}.\mspace{14mu} (7)}\end{matrix}$

Eq. (7) illustrates that the SNR is independent of the sample rate usedthroughout the transmitter signal generation and processing, but doesdepend on the update rate R. In addition, it should be appreciated thatthe SNR of Eq. (7) is similar to that achieved in amplitude modulatedand frequency modulated continuous wave systems, even though thetransmitted and received signals of FIGS. 2, 3, and 5 contain theinformation of a pulse.

In addition, it should be appreciated that the detection range of asystem employing the methodologies of FIGS. 2, 3, and 5 may be good. Forexample, the detection range of such systems may be equal to, or greaterthan, that of frequency modulated or amplitude modulated continuous wavesystems operating at the same average signal generator output power(e.g., the output power of a laser).

The methodologies illustrated thus far (e.g., the methods in FIGS. 2, 3,5, and 12) may be employed by any suitable system. For example, FIG. 1illustrates a system which may implement one or more of the methodsdescribed thus far. In addition, FIG. 7 illustrates a laser system,often referred to as a LIDAR system, which may implement one or more ofthe methods described thus far. The system 700 includes severalcomponents specific to the operation of lasers, such as a laser diodedriver and the laser itself. However, it should be appreciated thatanalogous systems may have the same general configuration, yet operatein a different domain (e.g., RADAR), by switching certain components.Thus, the methodologies of FIGS. 2, 3, 5, and 12 are not limited to usein laser systems.

As shown, the system 700 comprises a computing engine 702, such as adigital signal processor (DSP). The computing engine 702 may performvarious processing functions, such as performing one or more of the actsillustrated in FIGS. 2, 3, 5, and 12. For this reason, the computingengine 702 may include a periodic sequence generator 728 and a datareconstruction circuit 730. The periodic sequence generator may be usedto generate a code for modulating a continuous wave transmitter signal,such as has been described herein. The periodic sequence generator maybe configured to generate codes having lengths of between 512 and 4096sample points, or having any other suitable number of sample points, asthe various aspects of the invention are not limited in this respect.

The computing engine 702 is coupled to a digital-to-analog (D/A)converter 704, and in some embodiments the output of the periodicsequence generator 728 is coupled to an input of the D/A converter 704.Thus, the periodic sequence generator may provide a periodic sequence,such as a code, to the D/A converter 704, which may convert the digitalcode to an analog signal. The D/A converter 704 may be an 8-bitconverter, or may have any bit value. According to the non-limitingexample of FIG. 7, the D/A converter 704 is a clocked D/A converter thatreceives an input clock signal 703 having a frequency betweenapproximately 50 MHz and 200 MHz from a clock generator 705. It shouldbe appreciated that any clock generator and any clock frequency may beused, as the various aspects of the invention are not limited in thisrespect. In addition, the D/A converter 704 can have any suitablesampling rate, and in some embodiments the sampling rate may be variedto provide optimal SNR for a given processing power, maximum range, anddistance resolution of the system.

According to the embodiment of FIG. 7, the output of the D/A converter704 is connected to a laser diode driver (LDD) 706, which in turn isconnected to a laser 708, to drive the laser. The LDD 706 and the laser708 may be any suitable type of diode driver and laser combination, asthe various aspects of the invention are not limited in this respect.For example, the LDD 706 may be a 100 MHz LDD operating on approximately40-100 mA of current. Other LDDs may be used as well. The D/A converter704 may provide an analog version of a code to the LDD 706, which maymodulate the output of the laser 708 with the code. According to someembodiments, the D/A converter may be directly coupled to the laser,such that there is no LDD. Also, according to some embodiments, thelaser may be replaced with a light emitting diode, or other type ofsignal source

The system 700 further comprises projection and receiver optics 710. Theprojection and receiver optics may be configured to facilitatetransmission and reception of signals, and therefore may have anysuitable components for doing so. For example, the projection andreceiver optics 710 may comprise a lens 712 for facilitatingtransmission of a transmitter signal 714. The transmitter signal 714 maybe a coded continuous wave transmitter signal, having a coderepresenting a randomized version of a pulse modulating a continuouswave carrier signal. While a single lens 712 is shown, it should beappreciated that the projection and receiver optics 710 may comprisemultiple lenses, filters, or any other types of optics to facilitatetransmission of the transmitter signal 714.

The projection and receiver optics 710 may further comprise a lens 716,or any other suitable optics (e.g., additional lenses, filters, or otherforms of optics) for receiving a reflected signal 718. The reflectedsignal 718 may correspond to the transmitter signal 714 after beingreflected off one or more objects.

It should be appreciated that while the projection and receiver optics710 are illustrated as being within the same structure, as indicated bythe dashed-line box, systems according to some aspects of the inventionare not limited in this respect. For example, the projection optics(e.g., lens 712) and the receiver optics (e.g., lens 716) may becontained within distinct structures, may share one or more components,or may take any other suitable configuration.

The reflected signal 718 may be passed from the receiver optics, such aslens 716, to any suitable detector 720. The type of detector used fordetector 720 may depend on the types of signals being received (e.g.,LIDAR systems, RADAR systems, etc.) For example, the detector 720 may bea photodiode, an avalanche photodiode (APD), a photomultiplier tube, orany other suitable type of detector for the type of reflected signals718 being detected. Also, the detector 720 may be integrated with one ormore other components of the system 700, for example by being formed ona same chip as one or more of the other components.

The output signal produced by the detector 720 may be small in someembodiments. Therefore, it may be desirable to amplify the signal fromthe detector 720. Accordingly, in the system 700, the detector 720 iscoupled to a transimpedance amplifier (TIA) 722. The TIA 722 may operateat 100 MHz, with very low noise, e.g., with root-mean-square (rms) noiseof less than 2 pA/rtHz. However, other amplifiers with other operatingcharacteristics may also be used. In addition, while a TIA is oneexample of an amplifier that may be used in system 700, it should beappreciated that alternative types of amplifiers may be used in otherembodiments. In addition, in some embodiments no amplifier may be used.Furthermore, when an amplifier is used, the detector 720 may beintegrated on a same chip as the amplifier.

The output signal from the TIA 722 is an analog signal in thenon-limiting example of FIG. 7. To convert this signal to a digitalsignal, the output of the TIA 722 is coupled to an analog-to-digital(A/D) converter 724, which provides a digital signal to the datareconstruction circuit 730 of the computing engine 702 for furtherprocessing. The A/D converter 724 may be an 8 bit converter, a 12 bitconverter, or may have any suitable bit value. As with D/A converter704, the A/D converter 724 is a clocked converter in the non-limitingexample of FIG. 7, and receives the clock signal 703 at one of itsinputs. Thus, the D/A converter 704 and the A/D converter 724 may besynchronized. In this manner, the sampling performed by the D/Aconverter 704 may be synchronized with the sampling performed by the A/Dconverter 724, which may improve the accuracy of processing thereflected signal 718 to recover a code imbedded within the signal. Inaddition, as with the D/A converter 704, the A/D converter 724 may haveany suitable sampling rate, and in various embodiments the sampling ratemay be varied to provide optimal SNR for a given processing power,maximum range, and distance resolution.

The data reconstruction circuit 730 of computing engine 702 may receivethe digital signal from A/D converter 724 and process the signal torecover the pulse from the signal, for example from the code modulatedon the output of the laser 708 to produce the transmitter signal 714. Itshould be appreciated that the data reconstruction circuit 730 mayperform alternative, or additional functions as well, as the variousaspects of the invention are not limited in this respect.

As mentioned, the system 700 is a laser system, and therefore includescertain components (e.g., LDD 706 and laser 708) specific to operatingwith lasers. However, the same system structure may be applied todifferent contexts for operating on different types of signals. Forexample, the system 700 may be modified to operate as a RADAR system, orto produce millimeter wave signals having an approximate frequency ofbetween 30 GHz and 600 GHz, or to operate in other contexts, byswitching appropriate components. For example, the laser 708 mayalternatively be a radio wave generator, and the detector 720 mayalternatively be an antenna, rather than a photodetector. If thetransmitter produces millimeter wave signals having an approximatefrequency of between 30 GHz and 600 GHz, the detector may be a detectorcapable of detecting such signals. Other variations are also possible.

The system of FIG. 7 offers various benefits in terms of simplicity. Forexample, the system illustrates a direct connection between the TIA 722and the A/D converter 724. Furthermore, the system illustrates a directconnection between the A/D converter 724 and the computing engine 702.Thus, according to some embodiments, no mixer is needed either betweenthe TIA and A/D converter or between the A/D converter and the computingengine. Furthermore, according to some embodiments the D/A converter 704may be directly connected to the laser 708.

Furthermore, one or more of the components of system 700 may be formedon a single integrated circuit chip, or die. For example, the componentswithin dashed box 726 may be implemented on a single chip. However,other variations are possible.

Also, it should be appreciated that the system 700 may provide sharedaccess to certain data, or values. For example, as has been described,according to some embodiments methods for generating and processingtransmitter signals involve transforming a pulse into a non-pulse formwith a key, and then transforming a code of a received signal back intothe pulse using the key. Thus, according to an embodiment, thetransmitting portion and receiving portion of the system 700 may bothhave access to such a key (e.g., a plurality of phase values). Forexample, the key may be stored in a memory accessible by the computingengine 702, or may be accessible to the computing engine in any othersuitable manner, as the various aspects of the invention are not limitedin this respect. Alternatively, the key may be transmitted between thetransmitting portion and the receiving portion of the system 700.

As mentioned previously in connection with FIG. 6B, signalsreconstructed according to the methodology of FIG. 5 may have features,such as peaks, that fall between time intervals, or bins, of theprocessing system. In addition, as shown in FIG. 6B, reconstructedpulses may fall across multiple bins. It may be desirable to identifythe specific bin in which a reconstructed pulse peak falls. According toan aspect of the invention, a method for determining which of the bins areceived pulse falls into (e.g., see FIG. 6B) is provided. In addition,a method of determining the distance to an object with greaterresolution than that offered by the sample rate of the DAC and ADC(e.g., the DAC and ADC of FIG. 7) is provided.

In general, the smallest temporal delay of the reconstructed signal(e.g., the reconstructed delta function of FIGS. 6A and 6B) that can beresolved is given by 1/F_(S), which means the smallest distanceresolution Δz is given by Δz=c/(2F_(S)), where F_(s) is the samplingrate for sampling the received signal. However, the actual delay 2z/cmay be written as:

$\begin{matrix}{\frac{2z}{c} = {Q\frac{2\; \Delta \; z}{c}t^{\prime}}} & {{Eq}.\mspace{14mu} (8)}\end{matrix}$

where Q is the bin number (i.e., a whole number, such as 2, 3, 5, or anyother number), and (Δz)/c corresponds to the time duration of a bin.Thus, the reference t′ is the fraction of time the pulse is offset froma bin boundary. Thus, the peak of the reconstructed signal will occur inthe bin number Q. The amount of t′ can be determined as follows. First,the reconstructed signal, having a peak located at Q, is shifted, ortranslated, such that the peak is located at the origin. Suchtranslation of the peak to the origin may be performed in variousmanners, such as by translating the peak in the Fourier domain, or byany other suitable manner, as the methodology is not limited totranslating the peak in any particular manner. Then, the phase of theFFT of the shifted, reconstructed signal (e.g., the signal in FIG. 6B)may be plotted as a function of frequency, as shown by line 802 in FIG.8. The units of the horizontal axis are the frequency bin number of theFFT transformed signal, which is equivalent to units of 1/T, where T isthe duration of the sequence. The slope of the straight line fit 804provides an estimate of t′. The quality of this estimate is proportionalto the SNR, such that a higher SNR results in a better estimate of t′,which in turn implies that a very small fraction of Δz can be estimated.Thus, the distance to an object can be determined with greater accuracythan would be provided by the sampling rate alone.

The method described for determining the placement of a peak within abin may also be applied in situations involving multiple reflections ofthe transmitted signal, for instance as a result of the transmittedsignal reflecting from multiple targets. In such a situation, multiplepeaks are present in the recovered signal. The position of each peak maybe determined by zeroing all signals except in the vicinity of thepeak-of-interest and then applying the methodology just described inconnection with FIG. 8 to determine the location of that peak. The samemethod may be applied to each peak in turn to determine their locations.

The ability to estimate distance with greater accuracy than that allowedby the sampling rate alone provides various benefits. For example, theposition and the velocity of objects, which may be determined bymeasuring changes in position, may be determined with higher precisionthan would be allowed without the method described above.

The systems and methods described herein may be used in variouscontexts. For example, the ability to determine distance to an objectmay be useful in automotive applications, aerospace applications,surgical applications, archeological applications, astronomicalapplications, as well as others. In addition, various characteristics ofthe systems and methods described herein may facilitate useful operatingscenarios. For example, it should be appreciated that the methods ofcoding a carrier signal may be used to uniquely identify a transmitter.For example, a plurality of transmitters may each implement a method ofcoding a carrier wave signal with a code representative of a pulse. Areceiver receiving the signals transmitted by the plurality oftransmitters may identify which signal was transmitted by a giventransmitter if the code of that transmitter is known. In this manner,transmitters and receivers may be uniquely paired, which may facilitateoperation in environments in which there are multiple transmittersand/or receivers. According to an aspect of the invention, multipletransmitter signals may be multiplexed onto a single receiver.

The systems and methods described thus far may allow multipletransmitters to be multiplexed onto a single receiver. This is due tothe fact that the sequence period, or duration, T, can be chosen to bemuch longer than the maximum delay T_(max)=2z_(max)/c expected, wherez_(max) is the maximum expected distance to an object and c is the speedof propagation of the transmitted and reflected signals. Thus, multipletransmitters may each provide the same output signal (e.g., a signalcoded with the code of Eq. (2)), but with a different delay. Forexample, the delay, T_(d), may be given by pT_(d)>T_(max), where p isthe number of the transmitter (e.g., transmitter number two out offour), if p_(m)T_(d)=T, where p_(m) corresponds to the total number oftransmitters. Thus, Eq. (2) may be modified to account for this delay:

$\begin{matrix}{{s_{p}\left( t_{m} \right)} = {\sum\limits_{n = {{- N_{s}}/2}}^{{N_{s}/2} - 1}{\exp \left\lbrack {- {\left( {{n\left( {{\frac{2\pi}{N_{s}}m} + {p\frac{T_{d}}{\tau_{s}}}} \right)} + \varphi_{n}} \right)}} \right\rbrack}}} & {{Eq}.\mspace{14mu} (9)}\end{matrix}$

FIGS. 9A-9D show examples of the resulting signals 904, 906, 908, and910 for four transmitters for which N_(S)=1024. The units of amplitudeare generic units (u), which may be, for example, a voltage inmilliVolts, Volts, or any other suitable metric. The units of thehorizontal axes are the sample number. The signals are identical, exceptthat they are shifted relative to each other. In particular, the signal906 shown in FIG. 9B is delayed by 256 sample points from the signal 904of FIG. 9A. Similarly, the signal 908 of FIG. 9C is delayed by 256sample points relative to the signal 906 of FIG. 9B, and therefore by512 sample points relative to the signal 904 of FIG. 9A. The signal 910of FIG. 9D is delayed by 256 sample points relative to that of FIG. 9C,and therefore by 768 sample points relative to that of FIG. 9A. Again,each of the signals 9A-9D may be transmitted by the respectivetransmitters simultaneously.

For purposes of explaining how the multiplexing functionality may beachieved, it is presumed that the four transmitted signals shown inFIGS. 9A-9D are all reflected from an object. The reflected signals willbe received by the single received in the interval:

pT _(d) ≦t≦(p+1)T _(d)  Eq. (10)

The received signal 912 will thus be a combination of the four reflectedsignals, as shown in FIG. 9E.

FIGS. 9E and 9F illustrate that the received signal may be processed inaccordance with the methods described herein (e.g., according to themethodology of FIG. 5) to recover the four transmitted signals, and theimpulse modulated on each of the transmitted signals. The four impulses902 a, 902 b, 902 c, and 902 d (impulse 902 a is centered on the originand is therefore aligned with the y-axis) are separated by 256 samplepoints from their respective neighboring impulse(s), corresponding tothe delay between the transmitted signals. The regions labeled (1) thru(4) correspond to where the target reflections from each of thetransmitters may appear, i.e., if the delay between the impulses variedslightly from the 256 sample points used as an example.

It should be appreciated that while FIGS. 9A-9F illustrate themultipexing functionality with four signals, tens to hundreds oftransmitters can be multiplexed on a single receiver. In general, themaximum number of multiplexed transmitters, p_(max), may be given by:

$\begin{matrix}{p_{m\; {ax}} = \frac{\left( \frac{N_{s}}{F_{s}} \right)}{T_{m\; {ax}}}} & {{Eq}.\mspace{14mu} (11)}\end{matrix}$

Thus, as an example, according to one embodiment a multi-transmittersystem with a single receiver operates with an update rate R=10 Hz, asample rate F_(s)=125 MHz, and a maximum range of 100 m, whichcorresponds to maximum delay of 667 nanoseconds. Assuming a periodlength of the transmitted sequence of T=N_(s)/F_(s)=64536/125 MHz 525μs, almost 1000 transmitters may be multiplexed on a single receiver.

As mentioned, various operating scenarios may be realized byimplementing one or more of the methods and/or systems described herein.FIGS. 10A-10C illustrate three such examples. However, it should beappreciated that other operating scenarios are also possible.

FIG. 10A illustrates a scenario in which a single transmitter 1002 iscoupled with an array of receivers 1004, of which eight are shown.According to this scenario, the transmitter 1002 transmits a signal 1003which may be reflected by one or more objects 1006 a and 1006 b. Signal1003 may be a coded continuous wave signal, such as any of thosepreviously described herein. Each of the receivers 1004 may be capableof processing signals reflected from the objects 1006 a and 1006 b torecover the code. Thus, the distance from an individual receiver 1004 ofthe array of receivers to the reflecting object can be determined.

FIG. 10B illustrates an operating scenario in which eight transmitters1010 a-1010 h are coupled with a single receiver 1012. The transmittersmay each transmit a respective signal 1011 a . . . 1010 h. The signals1011 a-1011 h may be coded transmitter signals such as any of thosepreviously described herein. The signals 1011 a-1011 h may each be thesame as each other, may be the same except for different delays asdescribed in connection with FIGS. 9A-9F, or may be unique transmittersignals. The transmitter signals 1011 a-1011 h may be transmitted towardobjects 1014A and 1014B, which may create one or more reflected signals.The receiver 1012 may multiplex a plurality of reflected signals fromthe objects 1014A and 1014B to recover the codes on the reflectedsignals, for example as described in connection with FIGS. 9A-9F. Itshould be appreciated that while eight transmitters 1010 a-1010 h areshown, the scenario illustrated in FIG. 10B is not limited to use witheight transmitters.

FIG. 10C illustrates a scenario in which a single transmitter 1020 iscoupled with a single receiver 1022. The transmitter 1020 may transmit ascanning transmitter signal 1024, which may be used to scan a field ofview in which one or more objects may be present. For example, thetransmitter may emit a signal that is scanned across the field of viewillustrated by the arrow in the figure. The receiver 1022 may receiveany reflected signals from objects within the field of view, and mayprocess the reflected signals to recover a code imbedded in thetransmitter signal 1024.

It should be appreciated that the scenarios illustrated in FIGS. 10A-10Cmay implement any suitable transmitters and/or receivers. For example,the transmitters and receivers may be capable of transmitting anddetecting, respectively, laser signals. Alternatively, the transmittersand receivers may be capable of transmitting and detecting,respectively, radio frequency (RF) signals. Such scenarios may also beused with other types of transmitter signals. In addition, it should beappreciated that the three non-limiting scenarios illustrated in FIGS.10A-10C are merely examples, and that other operating scenariosimplementing one or more of the methods and/or systems described hereinare possible.

In addition, the methods and systems described herein may be used todetect multiple targets, or multiple reflections. For example, a singletransmitter may transmit a signal which undergoes multiple reflections,thus generating multiple reflected signals. A single receiver mayreceive the reflected signals and process them in accordance with one ormore of the methods described above to recover each reflected version ofthe transmitted signals.

It should be appreciated that various alterations may be made to themethods and systems described herein. For example, according to someembodiments, systems implementing an A/D converter and a D/A convertermay have variable sampling rates. The sampling rates of the convertersmay be varied to achieve optimal signal-to-noise (SNR) for a givenprocessing power of the system, maximum expected range of the system,and desired distance resolution. According to some embodiments, thesystems and methods described herein may be applied to short-rangedetection systems, and may also be used in long-range detection systems.In addition, according to some embodiments, a coded transmitter signalmay have a low ratio of peak power to average power, such as being lessthan approximately ten, or lower in some embodiments. Also, according tosome embodiments, the system 700 may not comprise a driver between theD/A converter and the laser. Rather, the output of the D/A converter maybe directly provided to the laser.

It should be appreciated that the methods described herein are robust.For example, FIGS. 11A-11B illustrate that the methods described hereinmay work even with transmitted signals that are clipped. In particular,FIG. 11A illustrates a coded transmitter signal 1102, which is codedwith a randomized version of an impulse. The y-axis represents theamplitude of the signal, in generic units (u). The signal 1102 comprisesa sequence having 1024 sample points. The signal is clipped. Theclipping effectively adds noise to the reconstructed signal. FIG. 11Bshows the reconstructed signal recovered using the methods describedherein, with the inset showing a close-up view of the reconstructedimpulse 1104. Thus, FIG. 11B shows that the transmitted impulse isaccurately recovered despite the clipping of the transmitter signal.

Having described several embodiments of various aspects of the inventionin detail, various modifications and improvements will readily occur tothose skilled in the art. Such modifications and improvements areintended to be within the spirit and scope of the aspects of the variousaspects of the invention. For example, several methods have beendescribed as implementing a Fast Fourier Transform. It should beappreciated that other forms of Fourier Transform may be used, and thatother types of transforms may be used. Accordingly, the foregoingdescription is by way of example only, and is not intended as limiting.The invention is limited only as defined by the following claims and theequivalents thereto.

1. A method of producing a coded continuous wave transmitter signal, themethod comprising: producing a continuous wave carrier signal; andmodulating the continuous wave carrier signal with a code to produce thecoded continuous wave transmitter signal, the code representing a pulsein non-pulse form.
 2. The method of claim 1, wherein the non-pulse formresembles noise.
 3. The method of claim 1, further comprising generatingthe code by transforming the pulse into the non-pulse form.
 4. Themethod of claim 1, wherein the code is a time-domain signal of the form:s(t)=IFT[FT[h(t)]exp[iφ _(n)]] wherein s(t) is the code as a function oftime, h(t) is the pulse as a function of time, FT represents a Fouriertransform, IFT represents an inverse Fourier transform, and φ_(n)represents a plurality of phase values.
 5. The method of claim 4,wherein the plurality of phase values φ_(n) is a plurality of randomphase values.
 6. The method of claim 4, further comprising generatingthe code by defining the pulse by a plurality of Fourier components tocreate a frequency domain signal, as given by FT[h(t)], adding a phasevalue of the plurality of phase values to each of the plurality ofFourier components to create a modified frequency domain signal, andperforming an inverse Fourier transform of the modified frequency domainsignal.
 7. The method of claim 6, wherein performing an inverse Fouriertransform of the modified frequency domain signal produces a pluralityof digital sample points, and wherein generating the code furthercomprises converting the plurality of digital sample points to analogsample points.
 8. The method of claim 4, wherein the code has a finiteduration, and wherein modulating the continuous wave carrier signal withthe code comprises modulating the continuous wave carrier signal withmultiple occurrences of the code.
 9. The method of claim 4, wherein thecode has a duration of between approximately 2 nanoseconds andapproximately 200 microseconds.
 10. The method of claim 4, wherein thecontinuous wave carrier signal has an approximately constant frequency.11. The method of claim 4, wherein the coded continuous wave transmittersignal is a laser signal.
 12. The method of claim 4, wherein the codedcontinuous wave transmitter signal is a radio frequency signal.
 13. Themethod of claim 4, wherein the coded continuous wave transmitter signalis a millimeter wave signal having an approximate frequency of between30 GHz and 600 GHz.
 14. The method of claim 4, wherein the codedcontinuous wave transmitter signal has a ratio of peak power to averagepower of less than approximately ten.
 15. A method, comprising:transmitting a continuous wave transmitter signal comprising acontinuous wave carrier signal modulated with a code representing apulse in non-pulse form; receiving the continuous wave transmittersignal; and processing the continuous wave transmitter signal to recoverthe pulse.
 16. The method of claim 15, wherein the code is generated bytransforming the pulse into the non-pulse form using a key, and whereinprocessing the continuous wave transmitter signal to recover the pulsecomprises using the key.
 17. The method of claim 16, further comprisinggenerating the code.
 18. The method of claim 16, wherein the keycomprises a plurality of phase values.
 19. The method of claim 18,wherein transforming the pulse into the non-pulse form comprises addingthe phase values to the pulse, and wherein processing the continuouswave transmitter signal using the key comprises subtracting the phasevalues from the continuous wave transmitter signal.
 20. A transmittingsystem, comprising: a computing engine configured to generate a code,the code representing a pulse in non-pulse form; and a signal generatorconfigured to produce a signal modulated by the code.
 21. Thetransmitting system of claim 20, wherein the code is a time-domainsignal of the form:s(t)=IFT[FT[h(t)]exp[iφ _(n)]] wherein s(t) is the code as a function oftime, h(t) is the pulse as a function of time, FT represents a Fouriertransform, IFT represents an inverse Fourier transform, and φ_(n)represents a plurality of phase values.
 22. The transmitting system ofclaim 21, wherein the computing engine is a digital signal processor.23. The transmitting system of claim 21, further comprising a clockeddigital to analog converter having an input configured to receive adigital version of the code from the computing engine and an outputconfigured to provide an analog version of the code.
 24. Thetransmitting system of claim 23, further comprising optics coupled tothe signal generator to facilitate transmission of the signal modulatedby the code.
 25. The transmitting system of claim 23, wherein thecomputing engine and the clocked digital to analog converter areintegrated on a same chip.
 26. The transmitting system of claim 23,wherein the output of the clocked digital to analog converter isdirectly coupled to an input of the signal generator.
 27. Thetransmitting system of claim 23, wherein the clocked digital to analogconverter has a variable sampling rate.
 28. The transmitting system ofclaim 23, wherein the signal generator is a laser.
 29. The transmittingsystem of claim 28, further comprising a laser diode driver having aninput coupled to the output of the clocked digital to analog converterto receive the analog version of the code, and an output coupled to thelaser to drive the laser.
 30. The transmitting system of claim 21,further comprising optics coupled to the signal generator to facilitatetransmission of the signal modulated by the code.
 31. The transmittingsystem of claim 21, wherein the signal generator is a light emittingdiode.
 32. The transmitting system of claim 21, wherein the signalgenerator is a radio frequency signal generator.
 33. A system,comprising: a transmitter configured to transmit a transmitter signalcomprising a continuous wave carrier signal modulated with a coderepresenting a pulse in non-pulse form; and a receiver configured toreceive the transmitter signal and process the transmitter signal torecover the pulse.
 34. The system of claim 33, wherein the code is atime-domain signal of the forms(t)=IFT[FT[h(t)]exp[iφ _(n)]], wherein s(t) is the code as a functionof time, h(t) is the pulse as a function of time, FT represents aFourier transform, IFT represents an inverse Fourier transform, andφ_(n) represents a plurality of phase values.
 35. The system of claim34, wherein the transmitter and the receiver are configured to haveaccess to the plurality of phase values.
 36. The system of claim 35,wherein the transmitter comprises a clocked digital to analog converterconfigured to receive a digital version of the code and produce ananalog version of the code, and wherein the receiver comprises a clockedanalog to digital converter configured to receive an analog input signalcorresponding to the transmitter signal and provide a digital outputsignal, and wherein the clocked analog to digital converter issynchronized with the clocked digital to analog converter.
 37. Thesystem of claim 36, wherein the transmitter further comprises a firstcomputing engine configured to produce the code and output the digitalversion of the code to the clocked digital to analog converter, andwherein the receiver further comprises a second computing engineconfigured to receive the digital output signal of the clocked analog todigital converter and process the digital output signal of the clockedanalog to digital converter to recover the pulse.
 38. The system ofclaim 37, wherein the first computing engine, the second computingengine, the clocked digital to analog converter, and the clocked analogto digital converter are formed on a same integrated circuit chip. 39.The system of claim 38, wherein the transmitter further comprises asignal generator driver coupled to the clocked digital to analogconverter to receive the analog version of the code and drive a signalgenerator, and wherein the signal generator driver is formed on theintegrated circuit chip.
 40. The system of claim 39, wherein thereceiver further comprises an amplifier configured to receive a signalfrom a detector and provide the analog input signal to the clockedanalog to digital converter, and wherein the amplifier is formed on theintegrated circuit chip.